This invention relates generally to gas turbine engines and, more particularly, to methods and apparatus for assessing damage to engines.
Gas turbines are used in different environments, such as, for providing propulsion as aircraft engines and/or for generating power in both land-based power systems and/or sea-borne power systems. During normal operation gas turbine engines may experiences large changes in ambient temperature, pressure, and power output level, and although such changes occur during normal operation, such change may result in undesirable changes in engine dynamics.
To facilitate maintaining engine efficiency, at least some known turbine engines include a controller that continuously monitors the engine to ensure that mechanical, aerodynamic, thermal, and flow limitations of the turbo machinery are maintained. However, despite continuous monitoring of the turbine engine, undesirable engine performance may occur without detection by the controller. For example, an erroneous actuator position feedback, or an obstruction in the afterburner duct may cause the variable exhaust nozzle (VEN) of a gas turbine engine to exhibit anomalous behavior that may not be detectable until a physical inspection of the VEN is performed. However, continued operation with the anomalous behavior may adversely effect engine operating performance.
Variable area exhaust nozzles (VEN) on gas turbine engines typically are manipulated to regulate a pressure ratio in the engine. Physically, the pressure drop across the nozzle changes in response to changes in the effective nozzle area, which may affect, for example, a fan operating line, and a core engine pressure ratio. Known VEN control logic can detect position sensor failure or actuator failure, however, more subtle damage scenarios, such as a hole resulting from ballistics damage, would be compensated for by manipulating the VEN position, but the damage is undetected by the control logic unless the needed compensation exceeds the physical limits of the VEN.